1. Field of the Invention
The present invention relates to an overhead cam shaft type (which will be hereinafter referred to as OHC type) internal combustion engine which permits efficiently supplying a lubricating oil into a valve mechanism provided on a cylinder head, and smoothly returning the lubricating oil from the valve mechanism to a crank case.
2. Description of the Prior Art
There is a known OHC type internal combustion engine which permits returning a lubricating oil, with which a valve mechanism including a cam and a valve arm provided on a cylinder head has been lubricated, to a crank case provided under a cylinder block, without passing the oil through a tappet provided in the cylinder block.
Such a type of internal combustion engine is provided with lubricating oil returning bores in that portion of the engine which is spaced from partition walls in the crank case, i.e. in the vicinity of rotating parts, such as a crankshaft and a connecting rod. Accordingly, return oil contacting and scattering from a rotating part, such as a crankshaft or a connecting rod, sticks to a side wall of the crank case so that the amount of consumption of lubricating oil is increased.
When a lubricating oil returning bore is provided in a position spaced from the crank case wall, the bore is away from the position where a head bolt is screwed. As a result, the tightening force of the head bolt applied to the cylinder head attaching portion is reduced so that the oil leaks from a gasket packing interposed between the cylinder head and cylinder block.
A lubricating oil returning bore also serves to recycle a blow-by gas, which leaks from a cylinder into a crank case, into a sucked gas, and guide the blow-by gas into a cylinder guide provided with a breather from which the blow-by gas is discharged into the atmosphere.
Since a blow-by gas upwardly flowing through the lubricating oil returning bore crosses therein the lubricating oil downwardly flowing therethrough, the returning of lubricating oil cannot be carried out excellently, or the lubricating oil is blown out from the breather.
A conventional internal combustion engine of this kind generally does not permit sufficiently supplying a lubricating oil into a valve mechanism.